Field of the Invention
The present invention relates to a crystal oscillator, particularly to an oven controlled crystal oscillator consisting of heater-embedded ceramic package, wherein the heater-embedded ceramic package establishes a symmetric thermal field to achieve good thermal uniformity.
Description of the Related Art
As shown in FIG. 1, the main portion of an oven controlled crystal oscillator is a ceramic carrier substrate 10 that is located in the central region of the whole oven structure. Respectively above and beneath the ceramic carrier substrate 10 are a simple crystal package 12 and an IC chip 14. The IC chip 14 includes a heater 16, a temperature sensor 18, an oscillator circuit, and a temperature control circuit. The IC chip 14 is coated with an overcoating filling 15. The crystal blank 20 is mounted in the cavity of the simple crystal package 12 and sealed with a metal lid 22. After crystal blank 20 and IC chip 14 assembly, the main ceramic carrier substrate 10 together with the simple crystal package 12 and IC chip 14 is mounted to a PCB substrate 24 by connecting solder 26, combining an exterior cover lid 28 to form an airtight chamber space.
In the oven controlled crystal oscillator, the heater 16 that is used to maintain the specific working temperature is integrated inside the IC chip 14. Another key element, temperature sensor 18 is also integrated inside the IC chip 14. The crystal blank 20 is heated by the heater 16 at beneath from the surface of IC chip 14 and through the ceramic carrier substrate 10 and solder 26. The structure is asymmetric with respect to the heater 16 therefore the temperature difference between crystal blank 20 and IC chip 14 is big, the temperature uniformity of structure is thus not good enough, so it affects the effect of controlling the oven temperature. As shown in FIG. 2, the temperature of the IC chip 14 is very close to that of the heater 16 when the oven controlled crystal oscillator works at an ambient temperature. The temperature difference between the crystal blank 20 and the IC chip 14 is 4.07° C. when the oven controlled crystal oscillator works at an ambient temperature of −40° C. The temperature difference between the crystal blank 20 and the IC chip 14 is 0.31° C. when the oven controlled crystal oscillator works at an ambient temperature of about 88° C. In other words, the temperature difference between the crystal blank 20 and the IC chip 14 is larger when the oven controlled crystal oscillator works at a lower ambient temperature. This is because the heater 16 transmits heat from the IC chip 14 to the crystal blank 20 to result in linear temperature gradient between them. The linear temperature gradient can establish an asymmetric thermal field and result in bad thermal uniformity.
To overcome the abovementioned problems, the present invention provides an oven controlled crystal oscillator consisting of heater-embedded ceramic package, so as to solve the afore-mentioned problems of the prior art.